1. Field of the Invention
The present invention relates to a method and apparatus for waste water treatment wherein waste water is treated with aerobic and anaerobic microorganisms simultaneously with exhaust gas treatment so that nitrogen-containing persistent chemical substances and nitrogen compounds can be treated to a high standard.
2. Description of the Prior Art
Generally, for the purpose of treating waste water in a factory, various treatment processes are employed according to the quality of the waste water. In some cases, chemical treatment processes are employed including neutralization, reaction, and coagulation processes. In other cases, biological treatment processes are employed including biological membrane, catalytic oxidation, activated sludge, special biological treatment, and anaerobic treatment processes. In still other cases, physical treatment processes are employed including precipitation, filtration, adsorption, floatation, and membrane treatment processes. Further, it is known to employ some of these conventional processes in combination to treat a high-concentration toxic waste water (see Japanese Patent Application Laid-Open Nos. H1-95000 and S64-43306).
In August, 1993, the Water Quality Bureau of the Japanese Environment Agency established an environmental quality standard and an effluent standard with respect to nitrogen (total nitrogen) and phosphorus. Hence, regulations on nitrogen (hereinafter nitrogen refers to total nitrogen) and phosphorus in effluent came into effect under the Water Pollution Control Law.
Earlier, nitrogen and phosphorus in effluent or waste water were regulated under more stringent prefecture standards put in force by any particular self-governing body.
It may be anticipated that the current control on nitrogen and phosphorus under the water pollution control law will be carried out in a stricter manner. Therefore, particularly for the treatment of waste liquids containing nitrogen in a larger amount, such as waste developer in semiconductor and liquid crystal plants, a need exists for a waste developer treating apparatus which can treat even a nitrogen content of such waste liquid and which is yet efficient and economical.
More specifically, there exists a need for such a waste water treatment apparatus as can treat waste liquid in one bioreactor not only with respect to such items as TMAH (Tetramethyl Ammonium Hydroxide) and BOD (Biological Oxygen Demand) in a developing solution, but also with respect to nitrogen in the liquid to a certain degree. With reference to waste developer in particular, a waste water treatment apparatus is needed which is capable of treating items such as TMAH contained in the waste developer in a high concentration, BOD, nitrogen, and surfactant (surface active agent).
However, the foregoing conventional methods for waste water treatment are simply intended to treat TMAH, and none of them are concerned with economical and reasonable treatment of nitrogen and/or surfactant.
FIG. 9 shows a conventional waste water treatment apparatus capable of treating nitrogen and surfactant and FIG. 11A is a system diagram for a conventional waste water treatment apparatus. The apparatus includes an anaerobic tank for treating the waste water with anaerobic microorganisms, two aerobic tanks for treating the waste water with aerobic microorganisms, a precipitation tank, and a filter tank. This waste water treatment apparatus, as shown in FIG. 11A, operates in such a sequence that an incoming waste water containing a development liquid is first anaerobically treated in the anaerobic tank, then aerobically treated in the aerobic tank, and then catalytically oxidized in the second aerobic tank, the sludge in the waste water being precipitated in the precipitation tank, the waste water under treatment being then subjected to filtration in the filter tank.
In addition, another conventional waste water treatment apparatus is shown in FIG. 12. This waste water treatment apparatus comprises (1) an anaeration tank 140 and an aeration tank (aerobic tank) 141 for treating TMAH and nitrogen compounds, (2) a catalytic oxidation tank (aerobic tank) 143 for treating a surfactant, (3) a denitrification tank 144 and a reaeration tank 145, (4) a filtration tower 148 for treating SS (suspended solids) and (5) an activated carbon adsorption tower 149 for treating coloring components. The waste water treatment apparatus comprises more treatment tanks than the treatment apparatus shown in FIG. 9, so as to clear the nitrogen regulation (regulation value: max. 120 ppm). The waste water treatment apparatus shown in FIG. 12 is the same as the waste water treatment apparatus shown in FIG. 9, in that it comprises the anaerobic tank 140, the aerobic tank (aeration tank) 141, the aerobic tank (catalytic oxidation tank) 143, and a second precipitation tank 146. On the other hand, the waste water treatment apparatus shown in FIG. 12 is different from the waste water treatment apparatus shown in FIG. 9, in that the former comprises a first precipitation tank 142, the denitrification tank, the reaeration tank 145, a pit 147, a rapid filtration tower 148 and the activated carbon adsorption tower 149. Accordingly, the waste water treatment apparatus shown in FIG. 12 has more treatment tanks by 5 in number than the waste water treatment apparatus shown in FIG. 9. This waste water treatment apparatus treats waste water as follows. First, the apparatus anaerobically treats the influent waste water containing developer in the anaerobic tank 140, next, aerobically treats it in the aerobic tank 141, and then treats it by catalytic-oxidation in the aerobic tank 143. In addition, the first precipitation tank 142 plays a role to accelerate aerobic treatment in the aerobic tank 141 by returning sludge to the aerobic tank 141. Water to be treated from the aerobic tank 143 is introduced into the denitrification tank 144 for denitrification. Water to be treated from the denitrification tank 144 is reaerated, and is introduced into the second precipitation tank 146. Sludge is returned to the reaeration tank 145 from this precipitation tank 146. Then, water to be treated from the second precipitation tank 146 has been introduced into the pit 147, and is furthermore introduced into the rapid filtration tower 148. Water to be treated which is filtrated in the rapid filtration tower 148 is introduced into the activated carbon adsorption tower 149 for treatment by activated carbon. Thus, this waste water treatment apparatus can treat waste water much more effectively than the waste water treatment apparatus shown in FIG. 9.
However, not to mention the conventional waste water treatment apparatus shown in FIG. 12, the above described prior art waste water treatment apparatus shown in FIG. 9 requires quite a number of treating tanks, including an anaerobic tank, an aeration tank and a catalytic oxidation tank as aerobic tanks, a precipitation tank, and a filter tank; therefore, the apparatus cannot be said to be an economical and reasonable waste water treatment apparatus.
In the past, at many industrial establishments and research laboratories, the treatment of persistent chemical substances including nitrogen and the treatment of exhaust gases have been separately considered.
The arrangement of a conventional exhaust gas treatment apparatus is schematically shown in FIG. 10 and FIG. 14 by way of example. This exhaust gas treatment apparatus is of such arrangement that the exhaust gas introduced is directed into a tank packed with plastic fillers, and that water as pumped up by a circulating pump is sprinkled into the plastic-filler-loaded tank. The exhaust gas is cleared of unwanted components as gas/liquid contacting takes place within the plastic-filler-packed tank which has been subjected to water sprinkling, the resulting treated gas being then directed upward.
Besides, as shown in FIG. 14, if three units of exhaust gas treatment apparatus shown in FIG. 10 are used, exhaust gas can be treated three times in quantity. The exhaust gas treatment apparatuses shown in FIG. 10 and FIG. 14 are effective for exhaust gases originating from acids, but not effective for exhaust gas containing organic substances. An exhaust gas treatment apparatus for exhaust gas including organic substances is shown in FIG. 13. This treatment apparatus consists of six activated carbon adsorption towers 151 in total. One of each two activated carbon adsorption towers 151 connected parallel is used as a spare. The activated carbon adsorption towers 151 adsorb organic substances. After adsorption of organic substances has been saturated with time, a spare adsorption tower replaces. While the spare adsorption tower operates, the saturated organic substances which activated carbon has adsorbed are removed by steam. This is why it is necessary to provide the spare adsorption towers.
In addition, another exhaust gas treatment apparatus Japanese Utility Model Laid-Open Publication No. H2-61424 has also been developed. However, the purpose to this apparatus is purely for treating exhaust gas and not for treating waste water as well as exhaust gas simultaneously. In addition, gas targeted by this apparatus is not exhaust gas containing organic substances but nitrogen oxides. In addition, this apparatus mainly uses activated sludge for treatment of exhaust gas, and does not have any conception to form biological membrane in fillers. It has no function to remove coloring components in waste water. Furthermore, another waste water treatment equipment is described in Japanese Patent Laid-Open Publication No. H4-305287. In this apparatus, a bioreactor is provided with a membrane filter. However, this apparatus does not have a structure for performing a three-dimensional anaerobic treatment process as preliminary treatment of membrane filter and vinylidene chloride treatment process. There have been a denitrification tank for waste water treatment Japanese Utility Model Laid-Open Publication No. H2-21000 and a treatment method for water including nitrogen compounds Japanese Patent Laid-Open Publication No. S53-35251. However, they do not treat exhaust gas as well as waste water as a total system of waste water treatment.
In this way, waste water has hitherto been treated by a waste water treatment apparatus, while exhaust gases have been treated, separately from such waste water treatment, by an exhaust gas treatment apparatus of such a system as scrubber, activated carbon adsorption, or combustion system.
However, the fact that a waste water treatment apparatus and an exhaust gas treatment apparatus are separately considered as in the past poses a problem because it can be a cause of reduced equipment efficiency at production facilities and/or research laboratories.
In case that waste water containing persistent chemical substances including nitrogen is of a high concentration, it is required that the waste water be diluted and, in order to carry out such dilution, it is necessary that constituent tanks of the waste water treatment apparatus, such as aeration and precipitation tanks, be larger in size. This involves increased initial cost.
For the treatment of production-related exhaust gases originating in chemicals (for example, organic solvents) used in production stages within a plant, and of odoral gases arising from waste water treating facilities, various treating systems are available including a scrubber system using a chemical and/or water flush, an adsorption system utilizing activated charcoal, and combustion system. Naturally, however, these systems involve great problems in respect of initial cost, running cost, management, and installation space requirement. Particularly, in an activated carbon adsorption tower, it is a problem that running cost is extremely high since extraction of activated carbon and regeneration thereof in a different place are required. In addition, if there is a great amount of exhaust gas to be treated, it is another problem that running cost becomes enormous.
In particular, semiconductor and liquid crystal plants may sometimes be confronted with complaints from people in the neighborhood by reason of odor arising from the plant even when the odor is of such a slight degree as will pose no legal problem. In such a case, basically a treatment apparatus for such odoral gas should be installed, but the problem is that installing a full-scale odoral gas treatment apparatus by reason of a small degree of odoral gas emission is uneconomical because it involves excessive cost burdens including construction, maintenance and management costs.
More particularly, a high-concentration toxic effluent from an existing semiconductor plant or liquid crystal plant, for example, a waste water containing a development liquid, contains 2000 to 10000 ppm of tetramethyl ammonium hydroxide (hereinafter referred to as "TMAH"), a substance having biological toxicity. Various surfactants are also included in addition to TMAH. TMAH is a compound comprised of carbon, hydrogen, nitrogen and oxygen as its molecular formula indicates. With nitrogen control in progress under the Water Pollution Control Law as revised, a rational and economical method for nitrogen treatment is required with respect to nitrogen compounds in water under treatment. Any anaerobic stage for denitrification will inevitably involve odor emission. Hence, efficient treatment of such odoral gas is strongly called for.
As earlier stated, at semiconductor and/or liquid crystal plants, any foaming due to surfactant in the water being treated or any odor emission from exhaust gases is a problem to people living in the neighborhood of the plant when considered from the view point of local environment maintenance, even if the foaming or odor emission is of a small degree. In particular, where the effluent stream for discharge of any treated water involving foaming due to surfactant is a source of agricultural water, the effluent is a great problem especially to the people in the neighborhood. In addition, the treated water is not apparently proper if it is colored yellow by coloring components (specifically resist components).
Generally, for the treatment of surfactant in the water under treatment at a final stage of waste water treatment, activated carbon treatment is in common practice. However, activated carbon treatment involves a problem that the life of the carbon is very short because the carbon is liable to a decrease in its inherent rate of adsorption after a given time period, and this necessitates withdrawal of the carbon for regeneration thereof. Recently, there have been developed various sorts of bioactivated carbon treatment apparatuses (see Japanese Patent Application Laid-Open Nos. H2-229595 and H4-260497). However, these apparatuses are primarily intended for the treatment of clean water of comparatively good quality and not particularly for time-consuming treatment of a waste water containing persistent surfactant. They use granular activated carbon, which involves high initial cost. Basically, they have no function to treat slight amounts of odoral gases and exhaust gases.
Meanwhile, the use of a granular activated carbon of the conventional system involves a problem that, since the activated carbon is of a granulated configuration, a failure to adjust the flow rate of back wash during a back washing operation may cause a mass of granular activated carbon to be washed away out of the apparatus.
Anyway, with such conventional activated carbon treatment apparatus as described above, it is impossible to rationally and economically carry out the treatment of a high-concentration toxic waste water containing persistent and less microbiodegradable surfactant in large amounts, as from semiconductor or liquid crystal plants, the treatment of such waste water being a time-consuming operation.
The reason is that since surfactant used in such plants are chemical substances of the type which is especially less microbiodegradable, the activated carbon, though it may initially adsorb and treat such agents to a certain extent, will rapidly come to the end of its service life, being no longer capable of adsorption for treatment. Even if a bioactivated carbon type apparatus is used, since the conventional practice with respect to persistent surfactant is such that the time allowed for contact reaction is only of the order of 2 hours, the contact reaction time is insufficient, it being thus impracticable to cause persistent chemical substances to be microbially degraded in an accurate and efficient manner.
In other words, with a conventional waste water treatment apparatus, even when activated carbon is utilized, it is not possible to more economically and more accurately treat high-concentration effluent discharged from such a plant as aforesaid with respect to slight amounts of surfactant, persistent chemical substances, the treatment of which requires more than 6 hours.
Naturally, it has been impracticable to treat waste water and waste exhaust gases simultaneously in an economical way.
According to certain experiments, when a high-concentration toxic waste water, such as waste developer, is treated without dilution and according to a conventional waste-water treating method, there are cases where there occurs a foaming phenomenon with the treated waste water due to a trace amount of surfactant present in the treated waste water if there exists a fall at the discharge point, even though the value of the treated waste water is considered to be well within a safe range under the state-of-the-art analysis techniques. Legally, this presents no problem whatsoever. Possibly, however, people living in the community may have a misunderstanding that treatment is still insufficient.
In the prior art, when such high-concentration waste water is treated without dilution and by increasing the concentration of microorganisms, because of the fact that both the microbial concentration and the waste water concentration are very high, there occurs a slight amount of odoral gas in the aeration tank during anaerobic treatment as well as during aerobic treatment. Where the quality of treated water is such that the water involves considerable foaming due to persistent surfactant, such treated water cannot be said to be quite safe to a bioecological system including such organisms inhabiting streams in areas of favorable natural environment as small fishes, and "Semisulcospicospira libertina", a kind of spiral shell, which serves as firefly feed. Such organisms in such areas generally have little power of resistance to environmental changes and, therefore, when a high-concentration toxic waste water is treated simply by a conventional method, they would not be able to live in such a treated water.
Treating high-concentration waste water without dilution involves presence of organic decomposition products in relatively large amounts, and the resulting treated water includes trace amounts of residual persistent surfactant and also trace amounts of residual organic substances. Conceivably, this may be the reason why aforesaid organisms could not live in such treated water.
There is known a method in which a high-concentration waste water is treated by being diluted about ten times, for example. However, this is not economical because it requires excessively large-sized apparatus.
Recently, a waste water treating system has been gaining popularity wherein the concentration of microorganisms is increased by utilizing various types of membrane filters. The use of such a system involves the problem of jamming with the membrane filter, and this requires periodical membrane cleaning, which adds to the cost and trouble of maintenance.
As stated above, prior-art waste water treatment apparatuses pose the following problems (1)-(5).
(1) (i) An anaerobic tank and aeration tank are used in treating TMAH, BOD and nitrogen contained in waste developer; (ii) a catalytic oxidation tank is used in treating surfactant; (iii) a filtration tank is used in treating SS (suspended solids); and (iv) an exhaust gas treatment apparatus is used in treating offensive odors and exhaust gases. This means a larger number of tanks required, say, an anaerobic tank, an aeration tank, a catalytic oxidation tank, a filtration tank, and an exhaust gas treatment apparatus, which poses the problem of high construction cost. When coloring components are treated by adsorption in the activated carbon adsorption tower 149 (refer to FIG. 12), the number of tanks increases and cost of the construction increases.
(2) Considering the quality aspect of treated water with respect to waste developer, the treated water may essentially meet the aforesaid regulatory control value. However, when the treated water is discharged into public waterways in an environmentally favorable district, if there exists a fall head between the discharge conduit and a public effluent stream, a foaming phenomenon may occur due to trace amounts of persistent surfactant, thus adversely affecting the scenic aspect of the environment.
(3) Any conventional waste water treatment apparatus is incapable of treating odoral gases and/or exhaust gases.
(4) Further, according to the arrangement of such a prior art treatment apparatus, it is not always possible to provide treated water of such a quality as will not adversely affect any aquatic life, such as small fishes or "Semisulcospira libertina", which are comparatively vulnerable to environmental pollution. This poses a problem such treated water may adversely affect global environment. More specifically, with treated water as obtained through the use of such conventional treatment apparatus, except that the treated water is diluted with large amounts of stream water and the like, even when the treated water meets the regulatory control value and involves no legal problem, the treated water may, as stated above, affect the bioecological system at discharge points in an area which has not suffered environmental disruption but is too scant of river water to sufficiently dilute the treated water, as recently often found with districts in which construction of a semiconductor plant and/or a liquid crystal plant is contemplated, so that there is a good reason to fear that the bioecological system which is vulnerable to environmental disruption may be destroyed. For example, according to the results of some experiments, when a treated water that meets the regulatory control value was obtained by treating a high-concentration toxic waste water without dilution and by employing aforesaid prior art apparatus and method for waste water treatment, aquatic organisms vulnerable to environmental disruption, such as small fishes and "Semisulcospira libertina", were not fully able to live in the treated water.
(5) Exhaust gases and persistent surfactant cannot be simultaneously treated and, therefore, an apparatus for treating exhaust gases is separately needed. This poses a problem that only for the treatment of trace amounts of odoral gases, the initial cost and running cost are exceptionally large.